舌運動の核上性支配—逆行性軸索流を利用した実験的検索

ON THE SUPRANUCLEAR CONTROLS OF THE HYPOGLOSSAL NUCLEUS:A MORPHOLOGICAL STUDY

　抄録　舌下神経核の核上性支配を検索するため，ラット舌下神経核に逆行性トレーサーであるHRPを限局的に注入し，ラベルされた神経細胞群をベンチジン法で同定した。延髄レベルでは，舌下神経核に近接した延髄中心核の背内側部と，一部三叉神経脊髄路核中間部に陽性細胞が見出された。延髄・橋移行部では，上下唾液核が分布する領域の小細胞性網様体にも見出された。橋レベルでは主に結合腕傍核に群をなして陽性組胞が同定され，さらに三叉神経主核と運動核の介在部にも陽性細胞が見出された。中脳レベルでは，中心灰白質外側と腹側部，また，　Edinger-Westphal核にも少数の組胞が同定された。比較的大きな舌下神経核とその近傍へのHRP注入例では，大脳皮質知覚運動領野の最腹側部に少数の陽性細胞が第5層にのみ見出された。しかし，この部に小破壊巣を作成し，Fink-Heimer法で変性軸索終末を延髄内に追跡したが，舌下神経核内への終止像は認められなかつた。以上の所見から，舌下神経核は脳幹の各レベルから多重の支配を受け，随意的運動のみならず，複雑な自動的運動を行なつていることが推定された。

Supranuclear controls of the hypoglossal nucleus were investigated in the rat, by means of retrograde neuronal labelling, following circumscribed micro-injections of horseradish peroxidase (HRP) into the hypoglossal nucleus. Retrogradely labelled neurons were found in the following structures.

1) Within the medulla oblangata, many reticular neurons in the nucleus centralis medullae oblongatae were labelled chiefly in its dorsomedial aspect. Some neurons in the dorsomedial aspect of the spinal trigeminal tract nucleus, pars interpolaris, were also labelled. Within the upper medulla and cau-dalmost part of the pons, a portion of the parvicel-lular reticular formation contained many retro-gradely labelled neurons, which were in close proximity to the territory of the inferior as well as superior salivatory nuclei.

2) Within the pons, the parabrachial nucleus contained many retrogradely labelled neurons in its medial as well as lateral aspects. In addition, the chief sensory and motor nuclei of the trigemi-nus contained retrogradely labelled neurons.

3) Within the midbrain, several neurons in the lateral and ventral aspects of the periaqueductal gray were labelled. A few small neurons in the Edinger-Westphal nucleus were also labelled.

4) Following larger injections of HRP into the hypoglossal nucleus and its adjacent structures, a few retrogradely labelled neurons were found in the 5th layer of the sensorimotor cortex, in its ventralmost region. Fink-Heimer silver impregna-tion method, following a small cortical ablation of the corresponding region, showed terminal degener-ation to be localized to the dorsomedial aspect of the spinal trigeminal nucleus, pars interpolaris, and its medially adjacent reticular formation. However, no terminal degeneration was found within the hypoglossal nucleus.

From above results, the hypoglossal nucleus re-ceives multiple imputs from the various brainstem nuclear groups. These structures appear to con-tribute to the elabolate automatic tongue controls, in addition to the cortically controlled glossal activities. These findings imply that the tongue movements often observed in an anencephalic and pseudobulbar paretic would be mediated through these multiple brainstem structures.